This invention generally relates to methods of determining positions of the head element in a storage medium assembly to maximize the accuracy of a read or write operation of that head element, more particularly the invention relates to methods of measuring the non-linear relationship between measured servo burst amplitudes and head position to improve the accuracy of the servo positioning system.
In a typical disk drive assembly, methods of determining head element positions to enable accurate read and write operations include having a servo writer write track and burst data information into each of various spoke regions distributed at radial intervals across each track of a disk medium. The track and burst information at each spoke region is then used to identify a corresponding radial position on that track. As illustrated in FIG. 1, a prior technique to determine a radial position of the head element on a particular track is to measure the read-back amplitude, or servo burst amplitude, and determine the amount of overlap of that measured head position (i.e., xm) to a pair of servo bursts, such as burst amplitude A 14 and burst amplitude C 16. When head element 12 overlaps equally both burst amplitudes A and C, i.e., amplitude measured for burst A equals amplitude measured for burst C (A=C), head element 12 is then considered centered over that track for an accurate write operation. However, with greater use of magneto-resistive (MR) heads in disk drives, typical servo burst amplitudes no longer vary linearly with cross-track position as was more common with inductive heads. The amount of non-linearity can vary with skew angle.
Thus, if the relationship between the head position to burst amplitudes is non-linear, then error in the perceived position occurs unless the disk drive assembly accounts for that non-linearity. Correspondingly, unless this non-linearity is taken into account in calculating the head position, an increased likelihood of errors in write and read operations can occur.
Various schemes have been proposed to address the problem raised by this non-linearity including methods of determining head element positions to enable accurate read and write operations. One technique provides a three pass track servo write to use smaller, more linear regions of the cross track profile. Yet another method would be to increase the number of burst combinations used so that each combination is used across only a quarter track instead of half track to provide another approach to use a smaller, more linear region of the head profile While these methods reduce the effect of the head non-linearities, they make no attempt to compensate for them directly.
There is therefore a need for an improved method of calculating the effect of the non-linearity of head element to provide more accurately measured head position for read and write operations in disk drives.
A PES linearization scheme using small excitation bode measurements is provided to account for non-linearity characteristics during measurements of head element positions so to generate a more accurate read and write operation by a head element of a disk drive assembly. The PES linearization scheme of this invention provides making gain measurements as the head element moves across the track, and then integrating the result to get a relative PES profile. By then finding two points on the profile a known distance apart, we can multiply the profile by the appropriate gain factor to get an actual PES profile. This profile can be then be used as a look up table to convert raw PES numbers into actual position.